Surgically implanted replacement or prosthetic hips are presently in widespread use. Conventional hip prostheses typically include a socket that is attached to the pelvic bone and an insert that fits in and extends from an opening in the upper end of the femur. The outer end of the insert carries a ball that rotatably engages the socket to simulate the patient's natural hip joint.
During the course of strenuous activities such as running, jumping, playing tennis and even walking, repeated large compressive stresses are transmitted through the replacement hip and through the patient's knee. The jarring forces that cause the stresses can, over time, cause the hip apparatus to loosen. Eventually, corrective surgery may even be required. Moreover, the repeated force of impact on the prosthetic hip can cause fractures and be very painful to the patient.
Various known replacement hips have attempted to address the above problems by employing cushioning or dampening substances between the ball and socket of the artificial joint. However, such devices do not significantly lessen the detrimental effects of repeated compressive stress applied along the replacement hip. Debris generated by the impact force exerted on the joint also contributes to loosening of the prosthetic stem. In particular, such debris causes the bone cells to produce a lytic hormone to attack and dissolve the debris. Unfortunately, this hormone also attacks and dissolves the bone, thereby loosening the stem.